This lens is tack sharp and that quality really shines with the medium format camera! Even wide open, this lens is extremely sharp all the way to the corners, it does improve very slightly when stepped up to 5.6 but the difference is so small that you really need to look very intensely at a blown up image to find it. Although this is a macro lens, it actually works very nicely also as a portraiture lens with very nice bokeh. In addition to the clarity of this lens, the image stabilization is a very nice addition. Due to the high pixel count on the medium format sensor, a person can be very restricted on the situations where you can hand shoot with this camera, especially if you are wanting to keep the ISO at 100, and so gaining at least 4 stops, if not 5, is very valuable and allows a person to shoot hand held a much greater percentage of the time.
I was worried when I got it, there was a muted rattle inside the barrel of the lens, turns out to be nothing, once the camera is on it doesn't make a sound except for the focus motor. Amazing lens, great for macro, and as a short telephoto. Highly recommended.
Super sharp and able to focus very close.